The present invention is related to a warp knitting machine having a weft thread insertion arrangement comprising two parallel transfer means which carry the weft threads on spaced holders and which are driveable in the direction of the needle bed; and a reciprocally moveable weft sled arrangement carrying thread guides to lay mutually crossing layers of diagonal weft threads subtending mutually opposed angles to the stitch rows.
In particular, the guides place the threads onto the weft thread holders, first to one of said transfer means and then to the other with exact and predetermined separations. The invention is further directed to a novel fabric having inlaid weft and warp inlay threads.
In a known warp knitting machine of this type, U.S. Pat. No. 4,395,888 to Wilkens, the sled carries weft thread guides which have an operative and an inoperative position. In the operative position the threads are placed in the openings between the weft thread holders. In the inoperative position the threads are led past the weft thread holders. When such weft thread guides are in their direction-changing position outside the holders the sled is displaced in a rearward direction by a number of holder divisions corresponding to the number of weft thread guides. This backwards movement is followed by an angled motion that this displacement is compensated out. If the weft thread guides are always in the operative position, there is provided a horizontal, parallel weft insertion. If they are brought for a time into their inoperative position, then a diagonal weft is provided. The number of weft thread guides is generally speaking 12, 18 or 24.
Another warp knitting machine is known (NL-OS 83 03 737) which comprises two weft threads each on a straight fixed guide upon which it may move in a reciprocal manner. The weft threads, at their turning position, are irregularly pressed into the spaces between the weft thread holders by a pressing rail. In order to provide a horizontal weft, the weft sled moves perpendicular to the direction of transfer. For the provision of a diagonal weft, the sled runs in the desired angle to the transfer means. Even here, it is necessary to utilize two weft sleds when it is desired to provide mutually crossing layers of diagonal weft thread.
Furthermore, a knitted fabric is known (U.S. Pat. No. 4,518,640 to Wilkens) in which, as reinforcing threads, two layers of mutually crossing diagonal weft threads, namely a warp inlay thread layer and a horizontal weft thread layer are bound into a knitted fabric. This gives rise to a thread structure which is extremely stable in all directions. Such a fabric can, for example, be covered with synthetic materials and thus serves as a matrix or as a laminate for the formation of synthetic forms of extreme stability. The inlaid threads can be of rather stiff material, for example, glass or carbon fibers. In order that the coating occurs in a regular manner and that even strength is achieved, the weft threads must be inserted in an exact and predetermined separation.
Since diagonal weft threads lead to a rise in the stability in the diagonal direction, they must subtend a substantial angle to the stitch wales, this angle should be at least 20.degree.. It is preferable that this angle be 45.degree.. However, it can be even greater, for example, as much as 70.degree..
Accordingly, there is a need for a wrap knitting machine of the heretofore discussed type which permits mutually crossing layers of diagonal weft threads to be placed in exact and predetermined separation, with just one weft sled. A greater number of weft thread sleds can of course be employed in addition.